The invention relates to thermoplastic polycarbonate compositions which are impact-modified with ABS type polymers.
The inventive polycarbonate (PC) compositions which are impact-modified with ABS type polymers are characterized by their excellent low temperature ductility, good processing properties expressed by relatively high melt volume rate (MVR) and good hydrolytic stability. Impact-modified polycarbonate compositions., e.g. those blends with ABS (acrylonitrile-butadiene-styrene polymer), are known for their high ductility at room temperature and low temperatures and good processing properties. However, for realization of demanding uses, in particular complex component geometries, it is often desirable to improve the processing properties further. Conventional measures lead to the desired improvement, however, as a rule cause a deterioration in the toughness. This is critical in view of fact that as high quality requirements of ductility, in some cases down to low temperatures, are as a rule imposed on components of PC/ABS, e.g. safety parts in automobile construction.
From EP 0 704 488 B1 PC/ABS moulding compositions are known with graft polymers which are based on a rubber polymer latex which has a weight median average particle diameter D50 from 0.20 to 0.35 μm. For using rubber polymer latices outside this range it is reported that especially the low temperature impact is significantly reduced.
From WO 01/62812 A1 the following composition is known. The composition contains two graft polymers and one thermoplastic polymer which can be described shortly as:                first graft of styrene and acrylonitrile monomers onto a first rubber latex with a D50 diameter of 80 to 228 nm whereby this rubber latex is provided by seed feed emulsion polymerization using a seed with diameter of 10 to 100 nm        second craft of styrene and acrylonitrile monomers onto a second rubber latex with a D50 diameter of 340 to 480 nm whereby this rubber is provided by seed feed emulsion polymerization using as seed the first rubber latex        rubber-free copolymer from styrene and acrylonitrile.        
It is reported that the grafts can be polymerized separately or can be produced in a common grafting of a mixture of the two rubber latices but from the examples only grafts are known which are polymerized separately. WO 01/62812 A1 mentions a number of thermoplastics resin, that can be used in addition to the styrene-acrylonitrile copolymer, including polycarbonate. However there are no specific examples of PC/ABS blends and thus it is also not taught in this document whether this composition would have beneficial results in PC/ABS blends. Moreover none of the examples has the parameters of the butadiene latices as used in the present invention.
Similarly from WO 01/62850 A1 compositions are known which are taught also to be suitable for PC/ABS compositions, The compositions contain a graft polymer onto a mixture of three rubber latices and a thermoplastic polymer which can be described shortly as:                graft polymer of styrene and acrylonitrile monomer onto a mixture of three rubber latices                    first rubber latex with a D50 diameter of ≦250 nm and a gel content of 30 to 95%            second rubber latex with a D50 diameter of >250 nm to 350 nm and a gel content of 30 to 80%            third rubber latex with a D50 diameter of >350 nm and a gel content of 50 to 95% whereby at least one of the rubber latices is produced by seed feed emulsion polymerization                        rubber-free copolymer from styrene and acrylonitrile.        
It is not taught that this composition would have beneficial results in PC/ABS blends. Again there are no specific examples of a PC/ABS composition nor do any of the examples meet the features of present invention.
Similarly from WO 01/62848 A1 compositions are known which are claimed also to be suitable for PC/ABS compositions. The compositions contain at least two graft polymers onto rubber latices and one thermoplastic polymer which can be described shortly as:                a first graft polymer of styrene and acrylonitrile monomers onto a first rubber latex with a D50 diameter of 230 to 330 nm whereby the third rubber latex is used as seed in the emulsion polymerization of the first rubber latex,        a second graft polymer of styrene and acrylonitrile monomers onto a second rubber latex with a D50 diameter of 340 to 480 nm whereby the third rubber latex is used as seed in the emulsion polymerization of the second rubber latex, and optionally        a third graft polymer of styrene and acrylonitrile monomers onto a third rubber latex with a D50 diameter of 10 to 220 nm,        rubber-free copolymer from styrene and acrylonitrile,        
It is reported that the grafts can be polymerized separately or can be produced in a common grafting of a mixture of the two or three rubber latices but from the trials only grafts are known in which the first and second rubber latices are mixed and then grafted together and the third rubber latex with a D50 diameter is grafted separately. WO 01/62848 A1 mentions a number of thermoplastics resin, that can be used in addition to the styrene-acrylonitrile copolymer, including polycarbonate. However, there are no specific examples of PC/ABS blends and thus it is also not taught in this document whether this composition would have beneficial results in PC/ABS blends. Moreover none of the examples has the parameters of the butadiene latices as used in the present invention.
From WO 01/66840 A1 PC/ABS compounds are known comprising the following components:                polycarbonate        with styrene and acrylonitrile grafted rubber based on at least two rubber latices whereas                    the first rubber latex has a diameter D50≦350 nm, preferably 260 to 310 nm, specifically 277 nm, and an gel content ≦70 wt.-% and            the second rubber latex has a diameter D50≧350 nm and an gel content ≧70 wt.-%                        rubber-free copolymer from styrene and acrylonitrile.        
Examples show that there is an improvement in properties like impact strength and elongation at break when a mixture of the above named rubbers are used compared to only one rubber latex with a diameter D50<350 nm. However, no data are submitted as to low temperature impact strength, and it seems also that there is still a lack in low temperature ductility. Accordingly low temperature properties still need to be improved, in particular, the balance of the properties like impact strength and ductility at low temperature is still to be improved.
From DE 196 39 821 A1 PC/ABS compounds are known which comprises the following components:                polycarbonate                    with styrene and acrylonitrile grafted rubber based on at least one ore more rubber latices whereas at the most 70 wt.-% of the rubber particles have a diameter larger than 180 nm.                        rubber-free copolymer from styrene and acrylonitrile or polyalkylene terephthalate.        
Examples show some improvements are visible with the filling pressure but it seems that there is still a lack in low temperature ductility.
Therefore, there is still room for improving the mechanical properties of PC/ABS compositions especially low temperature ductility, a good MVR and a good hydrolytic stability.